Coastal Zones: Dynamics, Landforms, and Human Impacts

Posted on Apr 4, 2025 in Geology

Understanding Coastal Zones and Landforms

Defining the Coastal Littoral Zone

The coastal littoral, or coastal zone, is the boundary between the sea and the continent. These spaces are very rich and varied from both physical and biological perspectives.

Key Coastal Zone Areas

Three distinct areas are recognized:

  • Supralittoral Zone: Extends from the high tide limit towards the interior of the continent. This zone is typically continental in character.
  • Mesolittoral (Intertidal) Zone: Lies between the high and low tide marks. This zone is narrower in inland seas with a small tidal range.
  • Infralittoral Zone: Extends from the low tide limit to where the distinct action of waves ceases. This zone is distinctly marine.

Classifying Coastal Types

Coasts can be classified based on rock homogeneity and geological history:

Homogeneous vs. Heterogeneous Coasts

  • Homogeneous Coasts: Composed of uniform rock types, often resulting in straight coastlines.
  • Heterogeneous Coasts: Composed of rocks with varying resistance.
    • Protruding areas: Hard rock forms cliffs.
    • Recessed zones: Soft rock forms bays and inlets.

Coasts of Immersion (Submergence)

Formed by sea-level rise or continental subsidence.

  • Examples:
    • Rias: River valleys flooded by the sea.
    • Fjords: Glacial valleys flooded by the sea.

Coasts of Emergence

Result from coastal uplift or sea-level lowering.

  • Example: Raised beaches situated above the current sea level.

Major Coastal Landforms Explained

Cliffs: Steep Rocky Coasts

Cliffs are steep, rocky coasts marking the transition between the mainland and the sea.

  • Typically formed from erosion-resistant rock.
  • The supralittoral zone is often narrow.
  • The base of the cliff is most intensely eroded by wave action.
  • Abrasion Platform: A nearly horizontal area at the foot of the cliff, representing the part of the continent eroded by waves.

Beaches: Soft Sediment Coasts

Beaches are coasts formed from soft, easily erodible materials, typically sedimentary, with a gentle slope between the mainland and the sea.

  • The coastal environment here is generally wider than on cliffed coasts.
  • Supralittoral Zone (Backshore): Often features dunes.
  • The boundary between the supralittoral and mesolittoral zones is marked by a sandy ridge (berm).
  • Mesolittoral and Infralittoral Zones: Are quite wide due to the gentle slope.
  • A major problem is beach destruction and erosion.

Deltas: River Mouth Deposits

Deltas are landforms, often triangular, created by deposition of sediment where large rivers flow into calm seas or lakes with low energy.

Estuaries: River Mouths in Energetic Seas

Estuaries are the mouths of rivers flowing into energetic seas capable of removing most incoming sediment.

  • River mouths are broad and deep, which facilitates the construction of river ports.
  • They can evolve and fill with sediment over time, forming wetlands.

Coastal Bars and Related Features

Coastal bars are sedimentary formations originating near the coastline. They can form:

  • Parallel to the coast.
  • Obliquely extending into the sea (Spits or Arrows).
  • Connecting an island to the mainland (Tombolo).
  • Isolating an inlet, forming a Lagoon or Albufera.

Dynamic Coastal Processes

Wave Action and Erosion

Wave movement is produced by the friction of wind on the sea surface. When breaking near the shore, waves acquire horizontal motion, causing sediment transport and coastal erosion.

Tides and the Intertidal Zone

Tides are the cyclic changes in sea level caused by the gravitational pull of the Sun and Moon. This process creates the intertidal (mesolittoral) zone.

Sea Currents: Sediment and Nutrient Transport

Sea currents are responsible for transporting sediments and nutrients in various directions, driven by changes in water temperature and salinity. We distinguish:

  • General ocean currents.
  • Rip Currents: Surface currents flowing perpendicular to the coast, generated by breaking waves.

Sea Level Fluctuations and Causes

Changes in sea level are usually not noticeable within a human lifetime. Key causes include:

  • Climatic Causes:
    • Glacial Periods: Ice accumulation leads to sea-level descent (negative eustatic movement).
    • Interglacial Periods: Ice melt leads to sea-level rise (positive eustatic movement).
  • Geological Processes:
    • Continental uplift can cause relative sea withdrawal.
    • Long periods of erosion can contribute to relative sea-level rise.

Human Impacts on Coastal Environments

Coastal Pollution Sources and Effects

Pollution significantly impacts coastal areas.

  • Causes:
    • Waste disposal.
    • Contaminated river mouths near coastal cities.
    • Industrial discharges and/or mineral oil spills.
    • Sewage discharges.
  • Small or enclosed seas are particularly vulnerable and can effectively become sewers.
  • Pollution can lead to eutrophication (excessive nutrient enrichment) in coastal waters.

Bioinvasions: Introducing Exotic Species

The introduction of non-native (exotic) species from different ecosystems can cause significant ecological impacts.

Overexploitation of Marine Resources

Excessive fishing (overexploitation) is a frequent problem in coastal zones. Consequently, many coastal areas are now declared as protected zones.

Landscape Alteration from Development

The construction of hotels, apartments, and other infrastructure is a very common impact, significantly altering the coastal landscape.